The present invention relates to a wireless communication apparatus, and, more particularly, to a method for reducing memory used for uplink (UL) Hybrid Automatic Repeat Request (HARQ) buffers.
FIG. 1 shows a wireless communication network 100 including a cell 102, which is a coverage area of an eNodeB 104. An eNodeB (E-UTRAN Node B or Evolved Node B) is the element in E-UTRA (Evolved-Universal Terrestrial Radio Access) of Long Term Evolution (LTE) that is the evolution of the element Node B in UTRA of UMTS (Universal Mobile Telecommunication System). It is the hardware that is connected to the mobile phone network that communicates directly with mobile handsets (UEs), like a base transceiver station (BTS) in GSM (Global System for Mobile Communications) networks. A plurality of user equipments (UEs) 106_0-106_N in the cell 102 are communicating with the eNodeB 104 through an uplink 108 and a downlink 110.
FIG. 2 is a conventional structure of HARQ buffers 202 and 204 in a memory unit 200 of the eNodeB 104. For example, in one UL HARQ process, with a HARQ ID HARQ-id#0, upon receipt of a data packet from the UE 106_0 through the uplink 108, the eNodeB 104 stores the UL data packet in a memory block 206 corresponding to the HARQ ID HARQ-id#0 and the UE 106_0. Upon successfully decoding the data packet, the eNodeB 104 sends an ‘ACK’ to the UE 106_0 through the downlink 110 to acknowledge the receipt of the data packet, and releases the memory block 206. If the data packet is not successfully decoded by the eNodeB 104, the eNodeB 104 sends a ‘NACK’ to the UE 106_0 through the downlink 110 to ask the UE 106_0 to re-transmit the data packet, and retains the memory block 206 for storing the re-transmitted data packet in a later HARQ process with the same HARQ ID. The eNobeB 104 also performs HARQ combining to combine the data packet and the re-transmitted data packet, and stores the combined data packet in memory block 208 to maintain integrity of data combining in case Channel Quality Indicator (CQI) or Rand Indicator (RI) measurements are invalid. The HARQ combining method includes Chase Combining (CC) and Incremental Redundancy (IR), which is known in the art. As shown in FIG. 2, the memory size of the UL HARQ buffers for Frequency Division Duplexing (FDD) system is calculated as below:UL HARQ buffers=2*number of UEs*number of HARQ processes*[maximum Code-Block (CB) size+tail length]*coding rate*number of CBs.
Since the conventional UL HARQ buffers in an FDD system are statically allocated for the UEs in the cell 102 and respective 8 HARQ-IDs of the UEs, the amount of memory for UL HARQ buffers increases linearly with an increase in the number of UEs supported by the eNodeB. It is therefore desirable to be able to allocate the memory used for UL HARQ buffers dynamically, so that more UEs can be supported by the eNodeB with limited memory size.